Modeling of particles impacting on a rigid substrate under plasma spraying conditions (original) (raw)
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Thermal Science, 2013
This paper deals with simulation of the spreading and solidification of a fully molten particle impacting onto a preheated substrate under traditional plasma spraying conditions. The multiphase problem governing equations of mass, momentum and energy conservation taking into account heat transfer by conduction, convection, and phase change are solved by using a finite element approach. The interface between molten particle and surrounding air, is tracked using the Level Set method. The effect of the Reynolds number on the droplet spreading and solidification, using a wide range of impact velocities (40-250 m/s), is reported. A new correlation that predicts the final spread factor of splat as a function of Reynolds number is obtained. Thermal contact resistance, viscous dissipation, wettability and surface tension forces effects are taken into account.
Thermomechanical Simulation of the Splashing of Ceramic Droplets on a Rigid Substrate
Journal of Computational Physics, 1997
sulting coatings have been studied by a number of authors [4,. The objective of such studies is to understand how Finite element simulation techniques have been applied to the spreading process of single ceramic liquid droplets impacting on a the properties of the coatings correlate with the parameters flat cold surface under plasma-spraying conditions. The goal of the of the production process. The present account addresses present investigation is to predict the geometrical form of the splat one fundamental issue that influences the final properties as a function of technological process parameters, such as initial of ceramic coatings; namely the heat transfer and material temperature and velocity, and to follow the thermal field developing flow phenomena associated with the impingement, spreadin the droplet up to solidification. A non-linear finite element programming system has been utilized in order to model the complex ing, and solidification of liquid droplets on solid cool surphysical phenomena involved in the present impact process. The faces.
Plasma Chemistry and Plasma Processing, 1995
The spreading and simultaneous solidification of a liquid droplet upon its impingement onto a substrate permitting thermal contact resistance has been numerically simulated; the effect of contact resistance and the importance of solidification on droplet spreading are investigated. The numerical solution for the complete Navier-Stokes equations is based on the modified SOLA-VOF method using rectangular mesh in axisymmetric geometry. The solidification of the deforming droplet is considered by a one-dimensional heat conduction model. The predictions are in good agreement with the available experimental data and the model may be well suited for investigating droplet impact and simultaneous solidification permitting contact resistance at the substrate. We found that the final splat diameter could be extremely sensitive to the magnitude of the thermal contact resistance. The results also show that for the condition of higher Reynolds and/or higher Stefan numbers the effect of solidification on the final splat diameter is more important.
Journal of Thermal Spray Technology, 1995
A measurement system consisting of two high- speed two- color pyrometers was used to monitor the flattening degree and cooling rate of zirconia particles on a smooth steel substrate at 75 or 150 °C during plasma spray deposition. This instrument provided data on the deformation behavior and freezing of a particle when it impinged on the surface, in connection with its velocity, size, and molten state at impact. The results emphasized the influence of temperature and surface conditions on particle spreading and cooling. When the substrate temperature was 150 °C, the splats had a perfect lenticular shape, and the thermal interface resistance between the lamella and the substrate ranged from 10− 7 to 10− 8 W/m2 · K. The dependence of the flattening degree on the Reynolds number was investigated.
Simplified 2D Thermo-Mechanical Modeling of Splat Formation in Plasma Spraying Processes
International Symposium on Advances in Computational Heat Transfer, 2008
The particles projected by arc plasma are generally of micrometric size (ranging in general between 10 and 100 µm) in conventional projection and their impact velocity ranges from 50 to 350 m/s. characteristic times for the formation of a splate are very short: less than 5 µs for the duration of spreading of the particle melted with a solidification which can start before the end of the spreading stage and continues in general between 0.8 and 10 µs after the impact.This work is devoted to studying numerically this complex coupling. The model is firstly validated in comparison with available results of particles spreading (large size and low impact velocity < 1 m/s).
The splat formation is one of the basic processes in thermal spray coatings. The performance of these coatings is strongly related to the process of spreading and solidification of molten droplets. The aim of the present paper is to simulate the fluid flow, heat transfer and phase-change that occur when a micrometric molten droplet impacts onto a rigid substrate and to examine the effect of the substrate conditions, such as initial temperature and material on the solidification time and spreading process. The effect of thermal contact resistance is also investigated. The simulation model used is based on the Navier-Stokes equations and the energy equation which includes convection and phase change. These equations are coupled with the Level Set function to track the interface between molten particle and surrounding air. The numerical model is solved using Finite Element Method and Comsol multiphysics 3.5a software.
Applied Surface Science, 2011
It is a 2D numerical study which treats the splat and flattening of the droplet during a thermal spraying process. An aluminum particle at a high temperature is impacted on steel substrate. A perfectly elastic-plastic model is used instead of the VOF method which is exclusively used in the literature. For this purpose, the finite element method with Ansys mechanical APDL program is used to solve the governing equations. Displacement, elastic and plastic strains, Von-Mises stress, energy densities, and contact pressure are evaluated during the impact of the particle. Additionally, it is found that the initial impact velocity has a significant effect on splat behavior. This mechanical model gives a promise results that can be improved to help understand the impact and flattening phenomenon.
Journal of Materials Science, 2006
An analytical model of the true area of contact between molten metal and a rough, solid surface has been used to calculate thermal contact resistance and to predict how it changes with surface roughness, substrate thermal properties and contact pressure. This analytical model was incorporated into a three-dimensional, time-dependent numerical model of free-surface flows and heat transfer. It was used to simulate impact, spreading and solidification of molten metal droplets on a solid surface while calculating contact resistance distributions at the liquid-solid interface. Simulations were done of the impact of 4 mm diameter molten aluminum alloy droplets and 50 lm diameter plasma sprayed nickel particles on steel plates. Predicted splat shapes were compared with photographs taken in experiments and simulated substrate temperature variation during droplet impact was compared with measurements.
Modeling droplet impact in plasma spray processes
Pure and Applied Chemistry, 1998
A model is described to predict the splat shape in plasma spray process. The results show that the impact process is comprised of spreading and recoil. The degree of spreading increases with Re 25; while spreading time is proportional to the ratio of the initial diameter to the impact speed. Under most conditions, simultaneous solidification plays a secondary role in arresting the spreading. Extension of the model to 3-dimensional situations and some preliminary results are also discussed.
Deformation behavior of a liquid droplet impacting a solid surface
The quality of coatings obtained by means of thermal spraying depends strongly on the mechanism of the interaction between the molten droplets and the surface to be covered. The aim of the present study is to simulate the impact of a droplet onto a substrate, in order to have a good understanding of the dynamics of droplets impact. In this study, the process of droplet spreading is described; the effect of impact velocity on the dynamic of impact is studied with a wide range of wettability. The pressure, velocity and spreading factor during the droplet spreading are reported. Finite elements analysis using the COMSOL multiphysics is used in this simulation. The results obtained are in excellent agreement with previously published results, experimentally and theoretically.